1. Field of the Invention
This disclosure is related to the field of polymer interlayers for multiple layer glass panels and multiple layer glass panels having at least one polymer interlayer sheet. Specifically, this disclosure is related to the field of acoustic polymer interlayers comprising multiple thermoplastic polymer layers.
2. Description of Related Art
Multiple layer panels are generally panels comprised of two sheets of a substrate (such as, but not limited to, glass, polyester, polyacrylate, or polycarbonate) with one or more polymer interlayers sandwiched therebetween. The laminated multiple layer glass panels are commonly utilized in architectural window applications and in the windows of motor vehicles and airplanes. These applications are commonly referred to as laminated safety glass. Its main function is to absorb energy, such as that caused by a blow from an object, without allowing penetration through the opening or the dispersion of shards of glass, thus minimizing damage or injury to the objects or persons within an enclosed area. Safety glass also can be used to provide other beneficial effects, such as to attenuate acoustic noise, reduce UV and/or IR light transmission, and/or enhance the appearance and aesthetic appeal of window openings.
The thermoplastic polymer found in safety glass can consist of a single layer of a thermoplastic polymer, such as poly(vinyl acetal) or poly(vinyl butyral) (PVB), that has had one or more physical characteristics modified in order to reduce the sound transmission through the glass. Conventional attempts at such acoustic dampening have included using thermoplastic polymers with low glass transition temperatures. Other attempts have included multilayer interlayers using two adjacent layers of thermoplastic polymer wherein the layers have dissimilar characteristics (see, for example U.S. Pat. Nos. 5,340,654, 5,190,826, and 7,510,771). These multilayer interlayers typically comprise a soft core layer having a single poly(vinyl acetal) resin having low residual hydroxyl content and two stiffer outer skin layer having a poly(vinyl acetal) resin having a significantly higher residual hydroxyl content. The soft core layer provides acoustic damping properties, while the stiff skin layers provide handling, processing and mechanical strength of the interlayer. The stiff outer layers generally contribute very little to the acoustic damping properties.
The residual hydroxyl content in the core layer poly(vinyl acetal) resin and the amount of the plasticizer are optimized such that the interlayer provides optimal sound insulation properties at ambient application temperatures for multiple layer glass panels, such as windshields and windows installed on vehicles and buildings. At temperatures above or below the ambient temperature, the sound insulation properties deteriorate significantly. For example, if the tri-layer interlayer composition is optimized such that the multiple layer glass panel comprising the tri-layer interlayer has a maximum sound insulation performance at 20° C. in its coincident frequency region (such as in the region around 5,000 Hz), changing the application temperature by about 10° C., such as decreasing the application temperature to 10° C. or increasing the temperature to 30° C., the sound insulation significantly decreases by several decibels or more. Further lowering or increasing the temperature reduces the sound insulation performance even more.
Multiple layer glass panels produced with conventional multilayer interlayers can have desirable sound insulation in one region of the world, but they can have lower or mediocre sound insulation in other regions of the world where the ambient temperatures differ. Even in the same region, as the seasons change in a year, the sound insulation ability of the glass panels also changes.
Accordingly, there is a need in the art for the development of a multilayer interlayer that has sound insulation performance over a broader temperature range. More specifically, there is a need in the art for the development of multilayer interlayers having at least one soft core layer that provides sound insulation performance over a broader temperature range.